First, I would seriously reconsider any advice to allow her to 'cry it out'. There are numerous articles and studies showing research where babies and toddlers who were forced to cry themselves to sleep suffered from serious mental and emotional issues lasting well into adulthood.
She is still a BABY. She is crying to tell you that something is bothering her. She may be getting ready to reach a new milestone, or cutting teeth, or going through a bout of seperation anxiety. All babies are different, and develop at different stages. At 7 1/2 months it is also very likely that she is going through a growth spurt, which would explain why giving her a bottle seems to help put her back to sleep.
Here are a few techniques that have worked wonders for me and my children when they were at that age:
-- keep lights off. This can stimulate her into full wakefulness. Use a soft nightlight, or a hall light with her door cracked when you go in to her.
-- try to have her in bed a little earlier. Most of the time, if a baby that age is put down past 8:30, they tend to be over-wound, which causes a shallow sleep pattern and easy wakefulness.
-- do not put her to bed on a full stomach -- I don't know of ANYONE that can sleep well if they're full -- maybe give a cracker and drink an hour or so before, make sure she has a clean diaper on, then quiet cuddles/reading will help settle her after.
-- if she seems a bit clingy, or her crying sounds as if she is frightened, as opposed to sleepy/cranky, she may be having nightmares. Cuddle and pacify as needed until she falls back asleep.
-- sometimes during seperation anxiety, putting one of your shirts in the bed with her will help her feel secure enough to self-soothe back to sleep.
-- if she is teething, I suggest using Hyland's brand Teething Tablets. They are all natural homeopathic, and run no risk of injuring her kidneys or overdosage as can happen with un neccessary Tylenol or Motrin usage. Tylenol or Motrin should only be used for fever. Hyland's can be found at most grocery, drug and Wal Mart stores. Look for the pink and blue box. (They make a lot of other great things for 'children's issues' as well)
-- if all else fails, try co-sleeping. Believe me, I wouldn't suggest it if it didn't work. You'll get WAY more sleep, as will she, and you'll build on her security and emotional strength, especially since you spend so much time away from her during the day, between working and school.
Feel free to email me if you need more information.
~S.