My cat is very skinny! Please help!?

So my cat gave birth to four kittens about 3.5 months ago. She has been a very responsible mother and she has only stopped feeding her kittens recently. She was already slim before giving birth but now she is really skinny. We did try to feed her high-nutrition kitten food but the problem is that she is not very willing to eat because she is very picky and she also saves her food for her kittens. There were times when we tried to feed her fresh chicken meat (she loves it) and yet she kept calling her kittens to come to eat it but didn't eat any herself. Afterwards every time when we feed her, we would feed her kittens at the same time as well so she would be willing to eat. But she never eats much. Besides, she does have some emotional issue. She cares a lot, almost too much about her kittens and spends a lot of time watching over them and sometimes even chasing her kittens so she can lick and clean them. And actually she is also experiencing some hair loss problem but it's not serious and noticeable so far. We are very confused and running out of ways to help her, so I would be very grateful if you can give me some possible suggestions or ideas! Thank you!