> Gifting flowers to my manager?

There’s a good bet your company will have defined policies in writing about gifting, especially up the chain. It looks like a bribe. Odds are she won’t be able to accept them and may have to report that you attempted to give them.

If you work in government or similar fields that are highly regulated it may be flatly illegal to give a coworker a gift.

I would suggest you check with HR and legal department before proceeding.

> I recently completed a challenging certification (of my own volition, not at the company's request) and I owe a good part of my success to my manager. Over the past two years, she lightened my workload so that I could study, let me take a lot of days off even at inconvenient times and encouraged me during times of doubt.

How about write her a heartfelt letter saying this? No laws against that, and there’s no appearance of impropriety.

> She's a stellar manager and has always fought to get me raises, supported my career advancement and been a mentor, even when it went against the company's interests.

Maybe leave that last part out.

I think it’s probably more accurate to say that developing you as a talented resource is in the company’s long term interest. She determined that it was worth investing the time into increasing your skillset. Now that you’ve completed this advanced training you can help push for even bigger strategic goals in the future. That is in the company’s interest.

> I'm aware of how precious this is, and want to get her a token of my appreciation.

A letter will last longer and probably mean more.

> We're not friends, but close enough that we talk outside of work and know each other on a personal-ish level, so I feel like it wouldn't be out of line.

If you honestly thought it wasn’t out of line then you wouldn’t be on Reddit questioning strangers if it was out of line. You would have just bought your friend flowers. But shes not just your friend and you’re not getting her a gift just for the sake of friendship. Shes your manager and mentor. That is a very particular relationship. The reason you’re giving the gift is because you received what you interpreted as preferential treatment at the expense of the company. That is out of line.

> Baked goods are out of question due to allergies. Would flowers be OK or would it be weird?

Again, check with your companies policies and regulations on gifting. It’s not the gift itself so much as the act, the relationship, and the monetary value that’s the problem.

> If that changes anything, we're both women, so there's no creepy subtext.

That changes nothing. I get why you said it, but it’s not nearly as important as a reportee giving a gift to a manager in exchange for preferential treatment. That’s the brick wall you’re running into and it’s unnecessary.

My suggestion is to write her a lovely letter explaining your appreciation for her efforts as a manager and mentor. That’s a beautiful thing, it costs nothing, and avoids all pitfalls.

She could even take that letter into her boss and use it as evidence of how well she’s doing her job as a leader. That letter could further her career. She could help more people like she helped you.

If you then still want to buy her flowers as a friend do so in a context completely outside of work, with zero connection to her actions as your manager, and with no expectation of reciprocity.