Remember her birthday is the primary thing. It doesn't matter how great you believe your memory to be, you can wake up the morning of her birthday and forget you have a gift and all these plans. Days can blur together, especially at the extremes of nothing much going on at all, and everything going on at once. You can think 'tomorrow' is her birthday and not realize it was 'today' until the day comes to an end and you 'discover' the error. Set alarms, set repeating notifications every hour if you have to, just do not forget.
Regarding spending Have you already established a price point for one or more gifts that she may be expecting? If you go 'cheaper' on a gift than you had in the past, she will notice. It almost doesn't matter what you've gotten for her, if it cost less than her gift last year, she will read into it. Either stick to a set cost for her birthday (gift, dinner, event attendance, whatever) and never vary from it, or always increase as a way to signify that you are more financially-sound than the previous year.
Don't worry, have alarms set! Usually buy online in advance. Wandering a mall with no idea what to buy is not good.
Price isn't an issue, something thoughtful is more important. For instance, cheap jewellery that is exactly her style would go down far better than a gold/diamond ring that was expensive.
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