I love Gracos. I researched lots online and looked at safety ratings and what other parents said about them, and I ended up getting a Triumph 5, and I love it! I'm not sure if they are still on the market though, as I got it about 3 years ago, but there has to be a similar one.
If there is one thing to splurge on, it's a car seat. Move your daughter right away from her infant seat, it's not safe! Convertible seats are great, sooner or later she will outgrow it and you will have to move up to a booster, but the convertible is safest for now. Don't go just with the highest safety ratings, they are often uncomfortable and bulky and/or hard to use. Listen to what the other parents have to say about them!
As for the grocery store, there is no reason why you can't keep the infant seat in the back of your car and use it only in the store.
There are people on here who are uneducated enough to recommend buying a car seat used and also to recommend keeping your baby in her seat as long as possible.
1. never buy a car seat used!!!! You never know if it was in an accident for one thing, for another, spend the extra money, this is the most important safety issue in your child's life!
2. You have kept your child in her seat as long as possible. She should have been moved before now. As a few other smart moms have mentioned, if you were in an accident, even a very minor one, chances are very good that she would sustain neck/back/chest injury because the seat is not a good fit for her!