At 3 years old, it might be hard to see/find ovarian tissue because its
probably hidden in fat.  You might have better luck getting all of the
ovarian tissue out if you can bring her in for the operation while she's in
estrus instead of some randomly scheduled appointment.  While she's in
estrus, ovarian tissue should be enlarged or swollen and easier to see/find
without a lot of exploration.

ORS is another reason why early age neutering is so much better for the cat
than traditional age neutering-- Young kittens have very little abdominal
fat-- the entire ovarian pedicle is easy to see and remove with virtually no
chance of leaving any remnant tissue.

You're lucky you found a different vet that will perform this surgery.  Most
vets won't do it and will just tell you to go back to the original vet.

Best of luck,

Phil