Very hard to say how it will work the kittens may like her straight away but she may not like them being all kittenlike.
First keep her in her carrier and let them sniff around and see how she reacts, if you have a cage even better.
If there is no adverse reaqction from anyone, I would let her out to wander the house, make sure she has some of her own things with her and her bed if she has one and see if that works. Make sure she has hiding pplaces like cardboard boxes.
If she is unhappy you will have to do proper introductions and keep her seperated from the kittens and gradually swap scents and rooms.
A feliway plug in may help.
Good luck and hope you MIL gets well soon