Can she do it or would it be disrespectful to the culture?
One thing that does bother them: wearing the red dot on the forehead and henna and saffron on the head at the hairline. Those have spiritual significance and unless you are given a dot in a temple as part of a wedding or other ceremony do not wear it. Small "bindi jewels" on the forehead are okay, but the red dot is not.
It depends on the situation. If it was as a costume it can be seen as disrespectful and a form of micro-aggression. However if it was to an event like an Indian wedding where they are the requested attire, it wouldn't be disrespectful at all.
it would be disrespectful