Every so often, I like to go off on a rant* about the “wedding etiquette” advice that you find on wedding boards, being handed out to brides by other brides who got the advice off other wedding boards — and who often have no knowledge of actual day-to-day etiquette. In fact, there is no such thing as “wedding etiquette”. The etiquette you use for your wedding should just be the very highest standard of everyday good manners and cultured behaviour that you use in your day-to-day life. The oft-cited rule that “anyone invited to wedding events should be invited to the wedding” is an example of internet-sourced “wedding etiquette”.
Standard etiquette throws weddings in with other ceremonial rites of passage like christenings, citizenship ceremonies, graduations and so were there is a ceremonial portion that is under the control of some administering authority (the law, the church, a university or so on) followed by a social gathering to celebrate — a single two-part event. Multi-month-long pageantry of multiple events is reserved for things like royal enthronements ant the Olympics. Standard etiquette does not permit people to orchestrate royal pageantry in celebration of themselves. Yes, there are such things as “showers” and “bachelorettes” that are clearly wedding-related — but they are properly small and informal, nearly impromptu fun-times arranged by close friends, not large formal parties.
On the other hand, what formal etiquette not only permits, but even insists upon, is that socially mature adults offer one another hospitality from time to time, in a network of gracious parties and dinners and return invitations, sometimes introducing guests of honour, sometimes just enjoying each others’ company. A hostess may at any time invite people to a party — which is generous of her! As hostess, she will go out of her way to make sure the guests have a good time, and as guests they will contribute to the pleasant occasion and be grateful to their hostess for providing it. This is NOT an imposition on the poor guests! But if they think it is an imposition, they are welcome to decline the invitation — and no, they do not have to bring a gift, ever, and usually SHOULD not.
So, your future mother-0in-law may, at any time, invite any people she wishes to invite over for tea (or brunch, or lunch , or dinner, or …) and she may if she wishes invite you to come as her guest of honour at that time so that she can introduce you to her friends. If she is very generous, she may invite some of your friends at your request in order to giver herself the pleasure of meeting them, and to introduce them to her friends. This is perfectly acceptable, and she may do so at any time.
What it is not, however, is a “pre-wedding event”. As you learned in kindergarten, you would never talk about a party in front of people who won’t be invited to it, so your wedding should not be a topic of conversation. If people ask about your wedding, you need simply turn the conversation gracefully onto something else. Talk about your hopes and expectations for married life, ask for housekeeping advice, talk about the transitions that are coming or about the customs of your husbands family that you are still learning — anything but centrepieces and chair covers and first dances. If you can do that, then you may socialize with whomever you want whenever you want and, whatever “wedding etiquette” may say about it, etiquette will have your back.