Here's what ended up happening....
Like Ky Kim suggested, I realized I could take the gift along in my purse (small photo album with a gift certificate in the first photo sleeve). That way, I could leave it if appropriate, and could take it back home if need be.
What happened is as soon as I walked in, I was greeted and welcomed and told how to find a seat and a mimosa, and then, even though the gift wasn't visible, the woman said that if I had brought a gift along, there was a table where they could be placed. Voilà! Problem solved!
The got married at 9:30 in a family-only ceremony in their home, which was originally the home of the woman's grandparents. I have no idea why the early hour, but I was happy about that, because, like so many people, I had a ton of other things to do that day.
Interesting side note: I didn't know anyone other than the woman who got married, so just found a table, introduced myself, and sat down and started making conversation. About 20 minutes later, come walking right past me was a woman I know pretty darned well, a friend of a friend, and we socialize pretty frequently. Turns out her daughter grew up with the bride, and they are really good friends. So she sat down at our table. Then, turns out, another lady sitting at our table was friends with my friend, because their husbands (both now deceased) used to work together.
Small, small world!