I also wish I was able to do the same. I'm more of a gusher than a squirter. My husband loves every second of it just the same.
I know being a woman myself , we want to know what we are doing is a good thing. Women hold back because we've always been taught not to do such things in the bed with our husbands. So letting her know while your in the midst of things how much you love it , and after she has squirted that its a good thing. While using he words " Good girl" or something else like " Oh, I love it, great job, I want more." Women have to be encouraged because we are so self conscience about ourselves to begin with.
In the throngs of passion I know I enjoy hearing from my husband the words " Good girl" while he rubs my body and hair softly. Now whether your wife may like that. I don't know. But lots of encouragement, continue to let her know how you love it and to maybe come up with a compromise of maybe at least one night not to hold back.
I will give her credit. I can hold it too, but its REALLY hard. So she's making a conscience effort to do it. Don't ever give up.