Have you tried speaking to her in a direct, but respectful way when she brings it up? I think that being direct is always more preferable than hinting at something. Or sometimes women say something in a way that they might think is “obvious”, but they don’t actually say it outright. It is not always obvious to the person listening, so speaking directly, but in a pleasant tone is always best.
Also, you might want to say it directly, but in a light/joking way so your mother doesn’t take offense.
For ex: Mother- Why don’t you buy yourself something nice for Yom Tov? Isn’t your husband taking care of you properly?
You – Oh, Mommy! You don’t have to worry. You married me off very well! I have the best husband in the world! I’ve been planning to get myself something when I can find the time. Anyway, I think my blue outfit still looks pretty good on me! No?
Hope that helps.