For a man to give any gift to a married woman, especially when she is an ex-girlfriend can be misinterpreted by her husband as an attempt to seduce her. And it can be provocative when it is an expensive gift that her husband has not given her like a trendy smart phone or tablet she does not have.
So, it is safe to be very cautious when buying and giving gifts to a married woman, especially when she is your ex-lover.
Of course only a man who is looking for trouble will give a married woman Victoria's Secret underwear.
And even giving her an expensive necklace with love pendant will also raise eyebrows.

If you want to give her books and magazines, you should give books on better marriage, housekeeping, gardening and family health and welfare. But don't giver her romance novels or pornographic Play Boy or Play Girl magazines.

It is best and safest to give her ordinary things like inexpensive pens, notebooks and cutlery or cooking utensils.

This matter is very important, because many men do like and even love married women as colleagues or friends and some of these married women can be very fond of their male friends and ask them for birthday presents or gifts for other occasions and if these male friends are not wise, they may end up giving their married female colleagues and friends the wrong gifts that can be misinterpreted as objects of seduction by their husbands and others.

I will advise every man whether married or single not give Valentine gifts to married women, except you have ulterior motives of dating them. And that will be clearly asking for trouble and lack of peace of mind.
You must never covet or want another man's wife.
You must not trespass the private property of another man.
Just keep off and go and look for yours.

It is also not wise for a married woman to accept romantic and erotic gifts from other men.
Any married woman who accepts an underwear, transparent nightgown or love jewelry from another man is either not wise or welcoming an extra marital affair.