If Maye knew where his daughter was, and if he was positioned so that nobody would be able to reach her without having to go through his line of fire, his tactics would not seem unreasonable. Indeed, if his daughter was sleeping, I would think leaving her asleep may have been prudent.
After all, if he grabbed her and set him beside him behind the bed, she might try to crawl away. Trying to maintain control over the baby and the pistol simultaneously might be dangerous and difficult. But if she's sleeping, and he can see that she's sleeping, then he doesn't have to worry about that.
Maye says he was crouched down behind the end of the bed to protect himself. The same bed that his child was lying on top of, he was using for cover.