How long of a grace period do tenants have when they are paying weekly

What does the agreement say? Are you the landlord or the tenant?

Grace periods are not required by law, so the lease determines if there is a grace period and what it is.

I am the landlord and the tenant has been late every week since she's moved in and she's told me that by law I have to give her a 5 day grace period

What is the wording in your lease?

We don't have a lease and we rent to her week to week just reciepts

1. Are they renting a room where you live or a rooming house? I ask because landlord-tenant laws in most states differentiate between the tenant renting a place themselves vs. renting a room in your house or a dwelling place.

2. If they are renting a place of their own, then most states will consider their occupancy (lacking a written agreement) as a "verbal month to month tenancy" and you can issue either
a) a notice that you are not renewing their tenancy (give them 30-days), or
b) issue a notice to move for non payment of rent (typically a 3-day notice, but it will depend on what state you are in).

ANY question on law needs to include your general locale as laws vary by area. Not sure how you expect us to verify what the tenant says is the law without knowing where you are.

But most places do not require a grace period. And 5 days on a weekly rental is ridiculous.

In general with no written agreement, there is no grace period.