Not knowledgeable about Omegas, but I can attest as a lady there are many things a cautious and careful lady can do to a watch without realizing its potential for harm, such as:
1/ spraying perfume on wrist (which can be done on a daily basis) while wearing watch;
2/ applying handcream while she’s wearing her watch.
Both those daily activities are hazardous to a watch (with risk of ingress through crown) if the watch is used and no longer water resistant.
If the change of the crown was not done properly, again risk factor.
As for the crown change, I would expect cost of no more than 50 euros incl parts and labor from a good independent in my country—
good Omega certified watchmakers in the UK have been recommended on the forum.