I felt the same too (I went from XS to L), what I did was to put away all the clothings I couldn’t fit so I won’t keep thinking about it whenever I open my cupboard. Bring her on a shopping spree if budget allows! Or if you know your wife’s style, surprise her with new clothings (pick those ruched flowy dresses (stretchy at bust).
I packed everything that doesn't fit and put it away and my husband took me on a fun shopping trip to buy new things! we had lunch and milk tea and it changes the mindset so well. also kept saying its an open trip and let's go anytime. the support helps!
Shop for more! That’s what happed to me.. she will feel better, telling her she looks good in those new maternity wear