I'm sure she's fine. Usually babies who are delayed in one area are delayed in so many, it's obvious.
So -
Does she hear? Does she respond when you speak or when there's a loud noise? Does she seem to respond to music?
She looks at you, she smiles - all great.
Does she focus on a board book if you hold her on your lap? Not that she follows the story, but does she look at it?
If you put her on the floor with one of those baby gyms or other objects above her, or in her crib with a mobile, does she look at these things?
She's already rolling from her back to her tummy - that's great! Not all kids do that at this age.
Babies do things in a different order from the next baby. Some babble all the time, some say nothing. Some roll over young, some don't. Some are easily startled, some are very calm. Some get teeth at 4 months, others don't get their first tooth until much later. Some have a full head of hair, others are little baldies. It's all normal.
You'll find these difference play out later on - some kids walk before they talk, some sit up sooner while others are still falling over, some potty train a year before others, some are active climbers and others are more exploratory on the floor. For example, my child was on his feet at 8 months, but didn't speak a word until 16 months. Other kids are just the opposite. He got his first tooth at 4 months, then didn't get the second for a very long time. Again, it varies.
Try to enjoy the miracle of all these milestones, and understand that for every thing your child isn't doing, she's doing a dozen other things. Don't miss those great moments because you're worried about one thing she's not doing yet. Even in kindergarten, their "report cards" check of skills with terms like "emerging" and "not yet" so that parents don't worry that certain things haven't happened yet.