Flowers are the default Mother's Day gift in the US, with roughly two-thirds of celebrating households sending or buying them. The default is fine but it is also the same gift she has gotten for years.
When flowers are still right. Recipients who have actively said they love fresh flowers. Long-distance gifts where the bouquet does the visual heavy lifting. Pairings (flowers plus a smaller picked gift) where flowers are not carrying the whole weight.
When flowers are not enough. First Mother's Day for a new mom (she does not have time to find a vase). Recipients who travel often (the bouquet wilts while she is away). Recipients who have explicitly said 'do not send flowers' (believe them).
The flower upgrade. A 3-month flower subscription ($90 to $180) extends Mother's Day past Mother's Day and shows up on her counter when she is not expecting it. The wow on day one is smaller than a single large bouquet, but the cumulative effect over 90 days is much larger.
The flower pairing. A single small bouquet ($25 to $45) plus a hand-poured candle ($35 to $50) plus a handwritten card. Total around $90, reads as more thoughtful than a $120 oversized bouquet.
What to avoid. Same-day flower delivery from app aggregators on Mother's Day weekend; you will pay 2x and the bouquet will look 1/2x. Stick with a local florist where you can call ahead, or a national subscription service that ships in advance.
The free upgrade. Whatever flowers you send, hand-write the card instead of using the typed default option. The card outperforms the bouquet in long-term recall by a wide margin.