"I want to thank you for taking the time to meet Mariam last week."
Here's why:
* "Taking the time to" is a common phrase used to express gratitude for someone's effort.
* "Meet" should be in the infinitive form ("to meet") after "taking the time."
* "Mariam" should be included as the object of the verb "meet."
* "Last week" provides context for when the meeting took place.