How to ask my wife when she's ready again

Me and my wife have wanted to start a family for a long time. We have been together since High School. We had saved up money for IVF and looked for a sperm donor. We had decided to go with an anonymous sperm donor. We were able to get 6 eggs from me. We talked about going the route of having twins, but decided against that lol. So we did the transfer and she got pregnant. Everything was good. Her betas was great. First trimester was a breeze for her. When she was 26 weeks she couldn't find the heartbeat on the doppler and I tried to find it, but couldn't. We had never had an issue finding it before so we decided to go to the ER just to make sure everything was okay. When they got us a room they took a look... Baby didn't have a heartbeat. It scared us both. After a while they told us she had to delivery the baby. Our poor boy was born sleeping. The worst part was they couldn't give us an answer to why it happened. We got our son cremated. It was hard for a long time. We both had to go to therapy, but slowly started to heal. It's been a bit over a year now and I am ready to try again, but I just can't tell with my wife. Some days she will talk about children like she can't wait to have her own, others, she will seem like she never wants to try again. I just can't tell and I'm scared to ask because it I don't want to upset her....