Hadrian's Wall Series by Jane Stain

Jaelle was furious at John. He'd left her for another woman. He'd also left all this junk behind. Wait, this helmet was interesting. Was it Roman? She had to try it on. Whoa, dizzy. Huh? Was this a cleverly disguised virtual reality headset? Because that looked like Hadrian's Wall. And the Romans on the other side didn't look friendly.

Previously certain her time travel trip was a hallucination, Jaelle changes her mind when a new exhibit at work features a piece of Hadrian's Wall with graffiti she created in the first century.

Talorac felt anxious about this meeting. A summons to the sacred grove had always meant the druids would perform their woad magic to prepare him for battle. So he was in no way prepared to make the acquaintance of the woman he found there with them. Deirdre was beautiful, and a warrior, and from the way she was flitting around the grove, she was the most powerful druid he had ever heard of in his life.