What to say when a first year PhD student can't handle basic courses? One of my first-year PhD students wrote to me saying that she is desperate as she is not handling her course load well (she is in the middle of her first semester), and she is afraid she will fail the courses.

There is no possibility of dropping the courses anymore and her funding is strictly dependent on scoring well on these courses.

Do you have any suggestions of what are good responses to this?

Edit: Thank you for your feedback. I think it's probably the case that she is not used to this level of intensity of the courses. I gave her a word of incentive, saying that me and the hiring comittee believed in her potential, so she should also. We also scheduled a face to face meeting.
I suggest having a discussion with the student to see if you can determine together what the issues are and figure out how to address them.  There are many reasons why the student may not be handling her courses well: personal issues, poor preparation, poor study habits, culture shock, etc.  It is also possible that she's not doing worse than other students, but her impression is negative because the courses/material is harder than her undergrad courses.  From what you have said, it's impossible to say whether she'll be able to do fine in the PhD program or not, or how much help she may need, but it certainly sounds like she could use at least some emotional support, if not tactical advice as well.

In addition, as Nate suggest in the comments, it may be helpful to diagnose the issue (for you and/or her) to talk to her instructors to get their impression of her in the courses.  If you have/know some reliable senior grad students, you might also suggest her to talk to them.