Not all females will go into heat by the book every 6 months. There is a good possibility that she is in heat. There is also a good possibility that she could go into heat and never show any visible signs. In any case, she should not be left where she and your male could possibly tie without you present. An unsupervised tie could be very dangerous for both her and your male. Plus, if you aren't there, don't know that they tied, how will you know if you need to prepare for a litter.
If I am doing the math correctly, your girl is only about 15 months old? She *may* not be ready to be a mom yet. This is where the expertise of your well seasoned mentor (you do have one of those, right?) will come in handy to help you determine if now it "the time" for her. IMO despite being good, valid concerns, some of the questions that you have asked are things that should be researched BEFORE you even consider breeding...not something that you pick up as you go along. And it's obvious that you love your girl and only want the best for her, which includes looking out for her best interest and properly educating yourself on this process.
Best of luck!