There are tow cultural things reflected in this phrase. It would be found, e.g. at the end of a letter.
1. gruessli means greetings. It is a form from the southern part of the German-speaking world, especially Switzerland. The diminutive li ending is typical there. Greetings are often included in the sign-off phrase of German letters.
2. There is always a filter how cozy we make a greeting. This greeting corresponds to the level of closeness reflected in signing your letters with Love, Laura. If this is not the closing of a letter, it might correspond to saying, "sending you my love". It does not have to be particularly intimate, just caring.
Best wishes, Nancy