Is a kegel exerciser a good gift for a friend who just had a baby?

Yes, but.... Perhaps giving the mom of a new baby the gift of your time might be even better. If you watch her child(ren) for just an hour or two, she can go for a walk, relax, shop. That often is enough so she could return refreshed to enjoy her baby. In addition, she might come back with renewed commitment to do kegels even without a device.
No, but nice thought. The otc kegel exercises are not necessarily the right way to do kegels. But encouraging her to pay attention to pelvic floor health is a great idea. Finding a local pelvic floor pt, would be a great gift.
Yes. Do it many times a day , as much as possible. It may take 4-6 months to notice effect.