Our hamster is about the same age (he has just turned two) and he looked a bit ropey after we were away for just 3 days. It's a change for them and maybe they go under a bit. In our case he wasn't eating properly and had stopped chewing chews, so his bottom teeth had got too long which then meant he was having difficulty eating. He also lost a bit of weight. Maybe give her a few days of feeding up and then take her to the vet if she seems a bit stronger.
So you could supplement with baby food, scrambled egg, a bit of porridge, crushed things like nuts.
I bought some Linwoods crushed pumpkin seeds and sunflower seeds, and some Linwoods shelled hemp and would put one of each of those out every 3 days or so (about half a teaspoon - I used the washed out lid from the baby food to put the crushed seeds/nuts in).
A lot of baby foods aren't suitable as they have onion, tomato or garlic in. These ones I found are ok and were in our local supermarket or in Boots the chemist - they are the 4 months age group baby foods (these tend to be less likely to have onion or tomato in):
HIPP Sweet Squash and Chicken (4 months version)
COW AND GATE Carrot and Lamb Hot Pot (4 to 6 months version)
Boots had a couple of good ones - fruity chicken and Sunday lunch I think they were. Just check the labels to make sure there are no spices, tomato, onion, garlic etc.
So each day I gave him a heaped teaspoon of baby food in a litte egg cup plonked in the cage (kind of pushed down into the substrate so it wasn't going to fall over).
Half a teaspoon of either: Crushed pecan nuts, Linwoods milled sunflower and pumpkin seeds, Linwoods shelled hemp, crushed walnuts, alternating them.
Still putting his normal mix out and the odd "extra" out as well - eg a tiny piece of cheddar cheese (thumbnail size) his usual piece of veg - broccoli, cucumber, carrot or cauliflower (thumbnail size), and maybe a few whole pumpkin seeds scattered in the cage too, to encourage still eating harder foods.
The Pecan nuts, Hemp seeds and Pumpkin seeds are all high calorie and help with weight gain - they are high fat but they are healthy fats. Hemp seeds have lots of vitamins and protein in as well. I also got the Linwoods milled wheat grass, which is just a powder and put that out in the baby food lid some days, mixed with a tiny bit of water - he wasn't too keen on that, but licked it up a couple of times (it's supposed to be chock full of vitamins and minerals).
Within a week to 10 days he had put his weight back on again.
It could be that she has some nutritional deficiency, or it could be some kind of illness, but often at this age, they start to have eating difficulties and that's why they lose weight and condition - toothache or overgrown teeth.
So maybe try feeding her up for a few days and see if she improves (our hammy loved his baby food extras - he would just have a few licks off the top rather than eat all of it).
It might be an idea too, when you do the clean - to lower everything to floor level - eg any toys, food bowl and water bottle, in case she is having problems climbing and getting to them. Either take levels out, or make sure there is nothing on them she could climb onto and fall off, or that there is nothing on the floor of the cage she could land on if she did fall off them. Maybe just do a partial clean for now so as not to stress her too much. Eg take the top half of substrate out but leave the bottom half and mix it in with the new substrate you add (or the clean half rather than the bottom half!) and leave the toys and wheel for another day. And leave her nest if you can - or leave part of it behind.
If she visibly improves a bit within a few days then maybe carry on with that for another few days and then if she seems stronger and like her old self, try and check her teeth or take her to the vets for a check over and a look at her teeth in case they need clipping.
The Linwoods milled things are sold in Holland and Barrett and Amazon sell them too (they're intended for human supplements lol). These are the ones I got
https://www.amazon.co.uk/Linwoods-Or...oods+sunflower
https://www.amazon.co.uk/Linwoods-68...words=Linwoods
https://www.amazon.co.uk/Linwoods-Or...woods+flaxseed
The pecan nuts and walnuts I just bought from the bakery counter in the supermarket and chopped them up with a knife into small pieces or squished them between two teaspoons.
It made our hamster's life more interesting for a while as well and he got quite excited finding the little egg cup and baby food lid with extras in each day. I alternated the Linwoods things with a different one each day in case there was something he didn't like. He seemed to like all of them but less keen on the flax seeds, so I didn't mix them.
I also got some Science Selective all in one hamster food and crushed/broke up into smaller pieces, a couple of those biscuits and just left them near his food bowl.
I'd also check her water bottle is working ok and she can reach it ok (hence lowering things).
Hope this helps (there were a couple of threads recently on supplementing hamsters and SKB had a lot of these suggestions). Still put the odd chew stick and normal hamster mix out though in case it isn't a teeth issue, to help keep the teeth trim.
I found our hamster was pouching his hamster food and hoarding it but couldn't chew it. They can lose weight quite dramatically if not able to eat.
I really liked the Boots range of baby foods actually and those two seemed to be ones he liked best (I think it was fruity chicken and a green one called sunday lunch or something).
Anyway, I thought Charlie was on his way out and he has now had a new lease of life after supplementing, then having his teeth clipped and is now eating normally again, but I still put the occasional bit of baby food out as a treat.
Note re the jars of baby food: Once open they need keeping in the fridge and using within 24 hours. I used to open a pot late afternoon/early evening to put the first day's amount out, put the pot in the fridge, use it again around the same time next day (ie 24 hours later) and then bin the rest (keeping the lids
which are useful for putting the crushed seeds in). Some people put all the baby food in ice cube trays when they open it and freeze it and just get a cube out each day to defrost - the jars I had were so small I didn't bother, but it would save a bit of money doing that (but more time and faffing).
Also the next morning you need to take out the bowl/egg cup or whatever, with the baby food in, from the cage in case they wake up and go and eat more, as it's been sitting there all night.