My sister in law hasnt been able to concieve after 5 years of trying and gets really touchy when take about having children comes up so we just try to avoid the subject when she is around. Im sure that it is really hard on her because you are going to do something that she wanted really bad but wasnt able. She will most likely be a little bitter when you do get pregnant but Im sure it will pass after all it will be her niece or nefew. Good luck, I hope everything works out.