Isla: would be my choice. Obvious pronunciation, and familiar.
Ayla: could be EYEla, could be AYla, would be both! Avoid.
Eilidh: no. Really, just no. Could be pronounced in a wide variety of ways, and the right way sounds sickly, as if she was ailing.
Ailish: I would prefer
Ailís, but I love
Alice and would use it without hesitation, so the issue wouldn't arise.