I was told no flying for 6 weeks after my stent, but maybe that was due to having instances of MI. Two years is ample time. A three hour flight is not long, it's classed as a short haul and shouldn't give any problems. If flying long haul for example 8 hours then a trip to the toilet as an excuse is a good move every couple of hours.
There is a guideline to follow when there has been a stent procedure but it is time sensitive and may not be applicable for your mother. If a person has undergone an angioplasty where a stent is placed in heart arteries, then a waiting period of one week is recommended before flight travel. The reason is the period immediately following the stent procedure carries a high risk of clot formation; air travel during this period would increase the risk further. However, it is recommended for some vulnerable individuals with cardiovascular issues to move about so as not to be positioned that could cause blood clots due in activity.
Thanks for the question. Take care.
I have on several occassions without any problems. I never thought about it.