Step 1: State the rule as a conditional.
The centre's rule says a member may spend at most one hour in the meditation hall. So if someone is meditating at Crossroads and following the rule, then their time is at most one hour.
Step 2: Note the given fact.
Shailaja has been in a meditation hall for at least one and a half hours, which is more than the one-hour cap.
Step 3: Set up the logic carefully.
Let $P$ mean she is meditating at Crossroads, and let following the rule require time at most one hour. Her actual time exceeds one hour.
Step 4: Apply the contrapositive.
If she is not violating the rule (time within one hour at Crossroads), then she cannot be the person who stayed over an hour at Crossroads. Since she did stay over an hour, the only way she is rule-abiding is if she is not at Crossroads at all.
Step 5: Reject the over-strong options.
We cannot claim she will be barred next time, nor that the hall is small, nor flatly that she is not at Crossroads, because each adds an assumption the statement does not support.
Step 6: Select the conditional conclusion.
The safe deduction is the conditional one: if Shailaja is not violating the rule, she is not meditating at Crossroads, matching option 4.
\[ \boxed{\text{If not violating the rule, she is not meditating at Crossroads}} \]