‘ехать ...на работу’ is standard for ‘to drive to work’ ‘заехать’ means ‘to drop by for a short time (in a car)’ ‘заехать за ней’ means something like ‘drive over to see her for a short time’, so “заехать за ней на работу» means “drive over to see her at her workplace for a short time”.

You should pick her up at work, take her back to your place where the table is already set with candles for dinner. Good luck!

In this context, заехать means 'to get someone from somewhere' or 'to stop for something somewhere'.

Preposition за ( + instrumental case) refers to someone/something you want to get or stop for.

Prepostition на/в ( + accusative case) refers to a place where you want to stop at.

It's за + instrumental, which is used among other things to express something that you aсquire:

Она вышла за газетой. She went out for (to get) a paper.

Он заехал за мной. He stopped by for me.

Он пошел за бензином. He went for (to get) gasoline.

https://www.alphadictionary.com/rusgrammar/for.html#za-ins

Literally it means behind or beyond:

Паша стоит за мной. Pasha is standing behind me.

Его поля за лесом. His fields are beyond the woods.

Даря живёт за городом. Darya lives outside town.

https://www.alphadictionary.com/rusgrammar/prepins.html#za

You must drive to work to pick her up.

It must be a word after "гтовый" - стол?- without such a word it has no sense.