This is a pretty common worry for parents at this age, but your mom is right. She won't starve herself, she will eat when shes hungry. It could be right now she just doesn't need the extra calories. She just might not be hungry! Children are very very good at regulating what they need to eat, and she is still pretty young.

Something you can do is monitor her weight to make sure she is not losing. Right now the average amount of weight for a baby her age to gain is 5.3 - 8 ounces/month. Is she still in diapers? Is she having lots of wets and regular poops?

Heres an excellent link from Dr Sears' Site for feeding picky toddlers.

http://www.askdrsears.com/html/3/T030800.asp
It may also be worthwhile to see if any new teeth are coming in - if they are and she is teething, she might be having some tooth pain which may make her not want to eat. Also check her mouth for white spots which could indicate a thrush infection. I know breastfed babies can get thrush but I am not sure about formula fed.

Also, I would REALLY caution against the force feeding. Forcefeeding can lead to the child getting negative feelings about food and possibly refusing to eat at all because they equate it with a negative experience.

You could always bring her to your pediatrician for an evaluation to make sure everything looks ok, but her eating will pick up with time.

((((hugs))))