I've cleaned up Arnika and have spent a good bit of time
trying to get my Pickpocketing skill up with my Bard. (I
don't plan on always having Myles.) It's at 18 now and after
a dozen tries of shoplifting 2gp sets of sling stones from
Anna and from Antone, I haven't succeeded a single time.
Pickpocketing works maybe 1:4 to 1:6 with Anna. The 50+ second
reload makes this process very time consuming. Any ideas on
what to do? I may need to level up a few times to get 21 or 24
before I begin to train it up but I have read posts here where
players get Myles up into the 50's in an hour and a half.

Thanks

I even noticed that with Myles the success rate was not very good until I reached about 30ish with level ups. If you want to avoid the save and reload, I would wait until you have leveled up a few more times. Although there is another possible solution if the NPC does not go hostile on you.

S
P
O
I
L
E
R

S
P
A
C
E

You can either use the Charm spell to make the NPC friendly again or give her back some of your ill gotten gains. I have done this with Anna, Braffit, Fuzzfas, and Heli since they are not immediately hostile. For some of the other NPCs such as Chief Gari or Antone, I waited until I had a much higher level of pickpocket.

spoiler
.
.
.
.
.
.
.
.
.
.
.
do He'li first until she's cleaned out. by then, your pickpocketing skill should be in the 30s region. then move on to Anna, then to Antone and Braffit. by the time you're done, you should be in the 50s regions. some save and reload may be required.