[souffle]

Perspex is not flexible so you would need to make a join.
The lethargy is a concern because if she has swallowed any of that plastic it could have caused a blockage or damage to the bowel. Has she been eating pooing and peeing OK?
When we work with perpex we use a stanly knife to score it then we carefully crack it over the edge of something like a table. As long as ths core is deep enough it should crack neatly. Just take care with the knife and measure out your piece of perspex. We would put one inside and one outside so you have a double layer of security.