Is there a limit to how many times you can use direct deposit for your refund

Why would you need that?  How many direct deposits are you expecting for the one federal return you can file and perhaps several states?

I just wanted to know for the future.
a friend wanted hers deposited and she was mailed a check. Is why I asked.

The limit is 3 per financial account per year.  See the full info below.

The IRS will not deposit more than 3 electronic refunds into a single financial account per year.

If your friend chose direct deposit and received a mailed check instead, here are 3 possible reasons:

The IRS says:

• We can only deposit refunds electronically into accounts in your own name, your spouse's name or in a joint account.
• A financial institution may reject a direct deposit.
• We can’t deposit more than three electronic refunds into a single financial account.

Than you for your help.

You're welcome.  Good luck.