Hate to say it, but your mom is right. She is more than capable to sleep all night at this age. My son has been sleeping at least 10 hours since he was 3 months old(we did sleep training with him) but did have an odd spell around 7 months that he wanted to wake up at 4am! So,after giving into it thinking it was this or that I realized it was a habit forming. I was making him be hungry at that time by feeding him. So, at first I gave him less and less over about 3 days so he was down to about half a bottle(ounce less each day) and then let him cry it out. It took just a couple day and he worked passed it. Your little one could be hungry yes, but probably only because you are encouraging the hunger by feeding her. Couple things to think about:Consisent bedtime routine that is different than nap time, bed time itself-too early/late,depending on what time she is waking anytime after 6am is considered normal(assuming appropiate bedtime),any light coming through that would wake her.
Hope that helps some! Good luck! It's not easy to hear them cry but sleep is so beneficial and needed for these little ones. Know that it's for her benefit and she can learn it's time to sleep. They CAN LEARN! =)
Letthing her cry is NOT showing her you are unreliable. They are able to learn and manipulate you by this age. You may see this when she may give a fuss then you look and she smiles! They know that you are going to respond...but when it's sleeping time it's important to have them learn that. My son snuggles and loves on me all day long-by letting him cry(at the time appropiate,because he knows how to sleep on his own we rarely have crying,ever)he does not feel abandoned by me.
*the book reffered I do not find "good"...I would try "Solve Your Child's Sleep Problems" By Ferber or "Happy Sleep Habits,Healthy Child" Both are excellent and good investments for later in child's life.
-K.