Hi A.: A couple of things I can share.
First of all, our little ones' cries will change in pitch and tone as they older and grow. Sort of like puberty (in essence, another growth stage.) I would check with the pediatrician, but I am fairly certain her new cry is normal. When my 3year old was an infant, he caught me off guard when his cry changed. I was driving and remember almost wrecking my car when I couldn't console him. Talk about nerve wrecking!! Just expect their cry to continue to evolve as they get older.
Now as to the crying at night thing. I know it's hard but you'll have to condition her to be able to sooth herself back to sleep. It will take time and you will be exhausted in the process BUT just remember, this will not last forever and she will outgrow it. (I remember wanting to punch someone when they told me, "Oh, it will just pass" because I was so tired but just hang in there -- it WILL pass).
I know it is heart breaking to let your baby cry in the other room but you're only training /conditioning her to expect to be picked up. It took me several days of sitting up in bed late at night, listening to the monitor and turning it down to let mine cry but he eventually got conditioned to going back to sleep (he's been sleeping through the night since he was 6 months old -- it took him longer b/c he was a preemie). Just remember - ROUTINE is your best friend. Babies and toddlers feel safer when they can predict what is about to happen (bath time, bed time, dinner time, etc.)
Try this. If you're sure she's ok (not sick, cold, wet, etc.) Go into her room at night when she cries but don't pick her up. Just pat her on the back (and do whatever sooths her -- kisses, whispering "Shh shh shh, it's ok, you're ok, mommy loves you" and walk out for a few minutes. Just contiue doing for a few days (3-4) that until she realized you're not going to pick her up. It's going to take a few days (for her to get the hint) and a stomach of steel to be able to NOT pick her up but if you want her to develop independence (and sleep!) you'll have to practice this "tuff love" technique. Best of Luck! You're not alone -- we've all been there. :-)