I feel your pain. My daughter is now 16, and probably did this until age 9. It sounds like you have tried the main avenues and they haven't worked. And from what you say, it sounds like you are pretty low key with her and not shaming her- you said she helps you with the sheets, not "make her do her own sheets." So unless I'm reading it wrong, you are doing just fine. If not, do make sure you assure her it's totally normal. And assure her that there are many other kids facing the same issue- she probably doesn't want to announce it to her class, and neither do others, so the more stories you can share that others her age and older deal with this as well will go a long way to normalize for her.
I think we ended up putting a mattress pad on top of the sheets so I didn't have to change the whole bed, just that. Also, you mentioned trying the alarm, but maybe give that another go in a while. My daughter is a heavy sleeper (like, sleeps through smoke alarms), so we found out that the alarm is more for us than her. :-) we started using the baby monitors again so we could hear when it went off. We'd shoot out of bed and rush in there to wake her up. That's the key- teaching her brain to wake up when about to pee. If we left it for the alarm alone to wake her up, no go. If we ran in to wake up her when we heard it, it worked like a charm. (minus the exhaustion by us!!) Two weeks I think it took, but we did it around age 9.
I would definitely advise against the medication. Lots of side effects and possibly a short-term solution. I'm no doctor, but our pediatrician felt this way as well as a panelist at a seminar I attended. At least not for many years, 7 is way too young IMHO.
So to recap- assure her that you know she hates this, but it's normal and she's not alone. And you are there to figure it out, but it might be a little while, and it's not her fault. Consider giving the alarm another try with you as the waker-upper. FYI, with the alarm, it won't always register in good nites because the moisture gets soaked up so quickly! So we had her wear underwear, clipped the sensor to that, and then wore a good nite over that.
Finally, if she is going to do sleepovers, we made it into almost a ninja challenge game. She didn't want the mom of her friend to know (I've heard stories of moms blabbing to the kids!!). So she packed a good nite into a plastic bag in her overnight bag, changed in the bathroom into pjs with pants (nightgowns can ride up and the other girls might spot the good nite). Then in the morning, she went to the bathroom again and put the wet good nite into the plastic bag she brought it in, and put it back in her bag to bring home to dispose. Instead of making it like a shameful hiding thing, I made it sound like a fun challenge, and she 'accepted' the challenge.
Good luck! She'll get it eventually, I promise! But I know it's a lot of work and worry for you, and a lot of upset for her. This too shall pass. If your ped makes you feel like it's a huge problem at this age, you may need to seek a second opinion.