If she was being completely honest, Artemis didn't mind that Wally forgot Valentine's Day.
Yes, it was irritating that he forgot about a day dedicated to love. For four years. In a row. But he always apologized when he realized he'd forgotten. He'd bring her flowers, chocolates, and once even jewelry to try and make up for it. He was always so cute, the way he practically wilting with guilt, his eyes looking at her pleadingly as he tried to explain why he'd forgotten yet again.
Even if she'd wanted to be mad at him, how could she not forgive him after that?
When M'gann and Zatanna gushed about what Dick and Conner had done for them (and in M'gann's case, Lagoon Boy at some point) she hadn't gotten even a little bit jealous because her boyfriend forgot to take her out or give her a present. Instead, she let a fond smile tug at her lips as they babbled, occasionally commenting when it seemed appropriate (though she wasn't even sure if they heard her-they always seemed like they were back on their date, reliving it). She knew she sounded the way they did whenever she talked about Wally's endless little romantic moments, which made her smile grow wider. When they asked her what Wally had done for Valentine's day, she'd just laugh, shake her head, and simply state 'He forgot' as if it were one of their inside joke. Which, in a way, she supposed it was. M'gann and Zatanna never understood why she didn't mind.
It wasn't just his apologies though. It was the way he acted. Every day, he'd come back to their apartment in California after his classes were over, and he'd kiss her cheek. He'd pet Brucely, ask her if she needed help in the kitchen, and never complained about the food (even if he thought Vietnamese spring rolls were extremely spicy). He was always showering her with affection and praise too. It was little things like this that reminded her he loved her. Not Valentine's Day.
So if anyone ever asked her why she didn't mind that Wally seemed to forget Valentine's Day every year, she'd tell them that to her, Valentine's Day was just a day on the calendar. Why should it matter if Wally forgot? He treated her like she was his Queen every day anyways. He loved her and she loved him. And they didn't need a specific day to show that to each other.
And besides, he did that on February 15th anyways. When he realized he'd forgotten again.