It has been quite a while since my two were that age, but I'll give this a shot.
At 7 months, she is exploring her environment and learning new skills. If she hasn't started crawling yet, she will be soon. Grabbing things is her way of exploring. She's not forming a bad habit (although it might be annoying to you right now). Soon, she will be walking and climbing, too. Guess what motivates her to learn how to do those new skills... ? Wanting to touch/hold the things that she sees that are out of her reach. Now, if she is grabbing for things that you don't want her having (knives, coffee cups, cactus plants, heirloom china, etc) then you need to put those things out of the way, and have things on hand that you can offer her instead.
People have different opinions about putting everything out of reach to spare themselves having to say "no" all the time (the proverbial candy dish on the coffee table), but that is a different subject from what you are talking about, correct? She's not running around the room grabbing things at will. At her age, it isn't really necessary to say "no" when she reaches/grabs at something she wants. If it is okay for her to have it, let her. If it is not okay, then let her know ("that can hurt you") and move it away from her, out of sight if possible, and offer her something else to be interested in. At 7 months she is probably still sitting nicely in the grocery buggy, but soon she will not. And then you will HAVE to say "no".
Saying "no" does not make you a "mean mother". It makes you a loving mother, who cares enough to set healthy limits for your child. The manner in which you go about it, however, could make you a mean mother. LOL
Distraction and re-direction will be your best friends. My son was constantly grabbing, climbing, struggling to get out of his stroller, etc.. He walked before 11 months and never wanted to be held (or held back!). I thought I would lose my mind. I dreaded trips to the grocery store b/c he was so busy and didn't want to sit still. But, you do what you have to do, and that means saying "no", it means enforcing "no", and it means giving them something else to keep their mind off of the thing(s) they can't have. At least until they are quite a bit older and are able to (slowly) learn self-control. Do it with love, and you are not being mean. Saying no can be very good. But at her age, you can't just say no and take the item away and let that be it. She will pitch a fit. Then you will really be stressed, no? Short simple words (That can hurt you, That can break, That's sharp, That's not ours, etc), remove the item (or move away from it) and offer an alternative. Distract, redirect.
Yes, it can make you go mad, but it will get better. Just try to remind yourself that she has fantastic motivation to learn new skills!!! :))
Enjoy these months, they go by so quickly~