To determine the pattern rule for Avery's spending, we analyze the amount of money she has left after each day:

1. Day 0 (before spending): $100.00
2. Day 1: $97.00 (spent $3.00)
3. Day 2: $92.00 (spent $5.00)
4. Day 3: $85.00 (spent $7.00)
5. Day 4: $76.00 (spent $9.00)

The spending amount each day increases by 2 dollars: $3.00, $5.00, $7.00, $9.00, ...

Pattern Rule:

Avery spends money according to an arithmetic sequence where the spending starts at $3.00 and increases by $2.00 each day. The total money left after each day follows this rule:

$\text{Money left after day } n = 100 - (3 + 2(n - 1))$

Or simplified:

$\text{Money left after day } n = 100 - (2n + 1)$

This rule gives the amount of money Avery has left after $n$ days.