I love piercing topics X3
As of now I have 31 piercings. 10 up each ear, rooks, tragus's, belly button, nose, tongue, snakebites, and two that wont be mentioned here.
In the lobes(what you want done), the pain is very minimal, but keep in mind that there WILL be some, as with any body modification.
With any piercing there are always risks. Infection, allergic reaction, growing out, things like that.
Infections are easy to avert so long as you clean your earring, but not excessively. 2-3 times a day is usually good, or any time something like a chemical or dirt comes in contact with them.
The reason I say not excessively is because if you clean them too often, you can get rid of the good bacteria that helps the piercing heal right.
Make sure you get them pierced with a metal you're not allergic to. For instance, the kind you have in your bottom *lower holes. Allergic reactions in piercings are NOT fun. Trust me on that one, lol.
Growing out isn't common for lobes, but it can happen. Mostly if you have an allergic reaction to the metal. Growing out is mostly a risk for surface piercings(belly button, nape, sternum, etc.).
As for convincing your mom, if you already have them done once and have taken good care of them, I don't think this should be too much of a problem. Unless she's already said no, which case I personally believe you should respect her decision.
Let her know that you'll take perfect care of them to avoid any of the risks mentioned above. That's the only thing I can really think of.
Ear piercings were easy for me to get away with because my mom has 3 in each ear. So I could always use the, 'you're a hypocrite' excuse.
It just depends on what your mom prefers. If she says yes, go for it. If she says no, just let it be.
*As pointed out, bottom could have been taken in a different way XD Therefore, it's been changed!
Thanks TM! Quote it X3
Then over the years I got an Industrial put in my ear, a nose ring and a lip ring. Had to take them all out when I got a new job.. I miss them 
