This looks fixable, it's a hard one but it can be done, it looks like her knee joint pin can't be taken out without some damage to the figure so the best bet is Loctite super glue, unfortunately this isn't cheap in Australia, almost $20.00 at Bunnings, and yet I bought it for $5.00 AUD in the US last year to fix my sunglasses while we were traveling there
If the original parts of that joint are still inside the knee then you will need the glue and a long pin, just need to dab an amount big enough so that it won't touch any other area inside the joint, then apply the lower limb fimly, it should set within a few seconds and by gently moving the joint back and forth the glue should set without locking then knee.
I hope this helps. This glue has saved me so many times for many years since I decided to buy it instead of the $2.00 crap that claims to be "super".