I just adopted a little guy, and he bit me really hard..right on the knuckle..my first bite where blood has been drawn...I instantly got nervous of him,
Luckily my boyfriend (Pillow on here) really helped me,
I held a little sprig of millet in my hand (although, with her being a syrian, you'd need a different treat, one she likes, but which she can eat from your hand) I held it pinched between my fingers (on a stalk, so he wouldn't have an excuse to bite me) and in doing so, when he ate the millet, he had to sniff my hand, and get used to my smell.
I fed him 3 sprigs of it in a row, then put my hand for him to sniff...you may be worried that she'll bite when you do it, but try and be confident.
If she has a seed stick or something, hold it in one hand, and tempt her with it, while making a little platform with your hand for her to stand on try and keep your hand steady, this should help her associate you with good things.
I did this to Alphonse like..twice a day, starting completely from scratch (because he was fully matured and very bitey, I thought it was best to be intensive with it)
it really worked for Alphonse, today he walked onto my hand with no bribe for the first time
Hope things work out for you and Mercades.