how did you delete her default gear???
Lydia does have problems with gear...
she does not 'see' enchantments...so she will not take enchanted bonuses into account.
works strictly off 'base damage'... even so she can randomly pick the worse item.
for me she is dressed all in enchanted ebony armor... and she wears it faithfully.
enchanted ring, necklace, and tiara... no problem
enchanted ebony shield and axe... she loves it.
(all items enchanted by me)
enchanted bow... no so much. give her enchanted glass, ebony, elven, dwarven she usually pulls out her original wood hunting bow.
however, give her an enchanted imperial bow and she uses it almost every time... (still randomly chooses her old hunting bow).
take enchanted ebony bow away then give it back she equips it immediately... she obviously knows it is better... but, after a few minutes she is back to hunting bow.... grrrrr!

oh.. as mentioned previously, if i leave her home for a couple days she takes off her ebony armor (chest piece only)... wtf???
p.s... have to be very selective in what i have her carry. so long as the items are lower base she seems to ignore them.