It depends on the context. If it's meant literally as a wife celebrating while naked, it's generally not appropriate in a public or family - friendly setting. However, if it's a more metaphorical use of 'birthday suit' to mean something like being in a natural or unpretentious state while celebrating, then it could potentially be okay, but still a bit strange - sounding.
Well, 'in her birthday suit' is an idiom for being nude. So if there's a story about a wife 'celebrates in her birthday suit', it could be a rather inappropriate or just a very unique and private kind of celebration story. However, it could also be a misnomer and not actually mean being naked at all. Maybe it's a creative way of saying she's celebrating in a very relaxed and unadorned state, like without fancy clothes or something.
If it's a story about a wife at a party in her 'birthday suit' (which might mean she's in her normal clothes, not literally nude as that would be inappropriate), perhaps the interesting things could be the unique style of her outfit. It might be a very fashionable or creative look that she has chosen for the party, which makes her stand out and becomes a topic of conversation among the guests.
Another great way to surprise her is by arranging a day full of activities she loves. For example, if she likes painting, take her to a painting workshop, then to a nice lunch, and end the day with a movie. Be creative and think about what she enjoys most.
If she looks great in her 'birthday suit' (again, assuming it's a regular, stylish outfit), it can definitely boost the mood. Her positive energy and confidence can be contagious, making others feel excited and happy to be there.
Well, typically in the official canon, Harry is not Voldemort's son. Fanfiction, however, allows for all sorts of unconventional storylines. So it's possible in a particular fanfic, but it's not the norm.
Surprise her with a hot air balloon ride. It's a unique and exciting experience that she'll never forget. You can arrange for a champagne toast while you're up in the air. Another way is to have a professional photographer secretly follow you both around for a day and capture all the special moments. Then present her with a beautiful photo album at the end of the day.
A simple and budget - friendly surprise could be to make a homemade coupon book. Fill it with things like 'one free back massage', 'a home - cooked meal of your choice', etc. It's personal and doesn't cost much.
On my wife's birthday, I planned a big surprise. I woke up early and decorated the whole house with her favorite flowers. Then I cooked her a special breakfast. Later, we went to the park where we first met and had a picnic. It was a simple yet very meaningful day.